Investment casting - ACME threads

[bk2]

Hello everyone,
I have heard that investment casting can be held to very close tolerances (+/- .005, sometimes tighter). If I have a STUB ACME thread called out in my part. Would they consider casting the thread form and later finish it out or do they cast the blanking dims and then machine the threads in a Lathe.

Thanks in advance for the replies

 

[arunmrao]

Investment casting parts can be cast with threads and then finished. There is no need to cast a blank and thread roll or machine them.

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[bk2]

Thanks Arun

Development Engineer
Oilfield Industry

 

[stanlsimon]

We just buy the threaded rod premade and chrome plated, then machine the ends as required. Why would you need to fabricate? Or are you talking about the female nut that screws onto it?

 

[plasgears]

One approach is to cast the threads on matching dies, and provide an undercut or flat at the parting line. No further finishing reqd. I designed a threaded shaft this way; very satisfactory.

 

[bk2]

Stanlsimon,
This part has a number of features and the STUB ACME threads are just one of them. We are trying to reduce the overall mfg cost by considering casting options.The part will have to be finished anyway because it has some sealing surfaces.




Development Engineer
Oilfield Industry

 

[Cockroach]

It can be done, casting of threads, but it is more common to cut or roll them off the shaft as a secondary process afterwards. Either way, there is no real difference in costing, particularly if the thread is machined numerically off a center.

I like to case harden by liquid nitration afterwards also. This gives me a nice hard finish and prevents thread pick-up in the mating part. On the print, specify "remove sharp edge from flanks of thread", that way the machinist will debur the sharp lip for you. If you thread roll, no worries on this.

Good luck with it.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada